Field
The disclosed concept relates generally to the generation and distribution of electricity by systems employing renewable energy sources, and, in particular, to a system and method for controlling and managing power ramp rates, frequencies and voltages in a renewable energy system that is to be interconnected with an existing electric power network (or electrical grid).
Background Information
The major resources for generating electricity on small islands (e.g., without limitation, Puerto Rico) have traditionally been in the form of fossil fuels, such as oil, coal, and natural gas. However, it is getting harder and more expensive to transport such fossil fuels to small islands for electricity generation. As a result, many small islands, like Puerto Rico, have looked to increase their utilization of utility connected renewable energy sources, such as solar photovoltaic (PV) systems and wind generation systems (commonly referred to as solar farms and wind farms), for electricity generation to supplement traditional fossil fuel-based generation.
However, solar PV systems and wind generation systems produce intermittent, variable power because the harvesting of the solar or wind energy varies with environmental factors such as cloud coverage, wind speed, etc. The intermittency of such renewable energy sources and the long distribution lines typically associated therewith often leads to undesirable voltage and frequency fluctuations in the distributed power system. The frequency problem is less severe for large utilities but the voltage issue exists. However, on small stand-alone grids such as those present on small islands for electricity generation, these fluctuations may lead to severe power quality issues leading to brown-outs, load shedding and, in extreme cases, complete shutdown of the generation and distribution system. As a result, small island power authorities, like the Puerto Rico Electric Power Authority (PREPA), have established technical requirements for interconnection of renewables with an existing electric power network (or electrical grid). Such technical requirements include requirements for managing rapid changes of the power output of the renewables (called “Ramp Rate Control”), requirements that mandate a minimum amount of power output by the renewables for responding to grid frequency changes (called “Frequency Response”), and requirements for controlling the voltage at the point of common coupling of the renewables to the distribution network to ensure that it meets predefined standards and limits (e.g., ANSI C84.1 or standards and limits set by the utility).
Therefore, there is a need for a system and method for cost-effectively controlling and managing power ramp rates, frequencies and voltages in a renewable energy system that is to be interconnected with an existing electric power network (or electrical grid).